In recent years, mobile terminals such as smart phones, tablet terminals and the like are rapidly becoming widely used. As a method of inputting to these mobile terminals, a method of operating a touch panel by a finger is generally used. On the other hand, in order to enable input to a terminal when both hands are full, model types that have a function for terminal operation by speech input are increasing.
In a mobile terminal provided with a touch panel, in order to avoid misuse, when the terminal is started up for the first time or is activated from a sleep state, an authentication screen is displayed and a confirmation is made as to whether or not the user is legitimate. Known methods of performing authentication and releasing usage restrictions include a method based on password input, or a method based on the locus of a finger on a touch panel, or the like.
In a case where a mobile terminal is inside a bag or a pocket, it is necessary to avoid a malfunction being caused by an unintended reaction of the touch panel. Therefore, a method is used wherein a particular operation that does not occur frequently on the touch panel is recommended to a user, and usage restrictions of the terminal are unlocked only in a case where the particular operation is accepted. The particular operation, for example, may be an operation of sliding a finger only a fixed distance on the screen, or an operation such as a double tap of a particular region.
Releasing usage restrictions on a terminal (that is, access restrictions to information or resources held by the terminal) based on user input to an authentication screen, a particular operation by the user, or the like, is referred to below as “unlocking.”
As related technology, Patent Literature 1 discloses an individual authentication device that uses biometric information such as fingerprint, voiceprint, face, or iris.
Patent Literature 2 discloses a method of unlocking a mobile telephone based on a result of comparing a stored user voiceprint and speech uttered by a user.
Patent Literature 3 discloses a speech recognition system in which an individual is authenticated based on voiceprint information extracted from inputted speech, and when authenticated speech is determined, commands from the speech in question are recognized, and a device is remotely operated by the recognized commands.
Patent Literature 4 discloses a mobile terminal device in which voiceprint authentication is performed based on speech generated by a user, and depending on the authentication result, prescribed processing is executed or halted in accordance with the speech.
PTL 1:
    Japanese Patent Kokai Publication No. JP2002-236666APTL 2:    Japanese Patent Kokai Publication No. JP2004-180254APTL 3:    Japanese Patent Kokai Publication No. JP2007-140048APTL 4:    Japanese Patent Kokai Publication No. JP2011-087110A